In a conventional railroad train braking system, each railway vehicle is provided with a brake pipe line which extends along the length of the vehicle. The pipe line is connected to the brake cylinders via the service and emergency reservoirs and various valves. Each end of the brake pipe is coupled to a "glad hand" connector by an angle or stop cock and a flexible hose. During the make-up of a train, the "glad hand" connectors are fastened together to form a continuous pipe line which extends from the head locomotive to the last vehicle of the train. The locomotive carries an air compressor or a source of compressed air that is conveyed to the brake line through various valves which include one or more master control valves which are in easy reach of the locomotive engineer.
Now when a train is made up and the "glad hand" connectors of each vehicle are interconnected to each other, the angle or stock cock on the tail end of the last vehicle is closed while the remaining cocks are opened. Thus, a continuous closed brake pipe line is formed from the foremost locomotive to the rearmost vehicle. The brake pipe is pressurized or charged from the air compressor on the locomotive to a predetermined pressure level, such as, 90 psi, for freight operation. The predetermined pressure in the brake line causes the pistons in the brake cylinders to be withdrawn on each railway vehicle so that the brakes are released and results in charging of the respective reservoirs.
Now when it is necessary or desirable to initiate a brake application, the engineer in the lead locomotive cuts power and actuates the master control valves which causes a reduction in the pressure in the brake pipe which is sensed by the control valve carried by each vehicle. When the differential pressure between the reservoir and the brake pipe exceeds a predetermined amount, the control valve causes the piston of the brake cylinder to extend and apply the brakes in proportion to the magnitude of the differential pressure. When a brake release is desired, the engineer actuates the master control valve in the locomotive cab to cause the build up of pressure in the brake pipe line to the full release value, namely, 90 psi, or to some intermediate pressure level if a partial brake release is appropriate.
Further, the advent of cabooseless trains now requires that the brake pressure in the last vehicle of the train be constantly measured and checked to insure safe operation. The removal of cabooses from the tail ends of the freight trains has generated a need for equipment which is capable of sensing and monitoring the brake line pressure and the presence of the last vehicle. In actual practice, the equipment includes the electronics, the radio transmitter, the battery supply and the pressure transducer which are all housed within an appropriate protective casing. It has been found that one of the most practical locations for mounting the equipment casing is on the end coupler of the last vehicle since the "glad hand" connector of the brake pipe hose is readily available for measuring the existing air pressure. It will be appreciated that the coupler of the last vehicle is obviously the end-of-train and that the equipment is somewhat protected by the body of the vehicle against the harsh environment of railroading. The monitoring equipment is coupled to the "glad hand" connector via a coupling and a flexible hose. The conventional "glad hand" coupling at the end of the brake pipe hose of a railway vehicle will provide a secure connection resistant to excessive leakage only when it is connected to another "glad hand" equipped with a mating gasket. Also, these "glad hand" couplings are so constructed that, whenever two "glad hand" couplings between adjacent vehicles are connected, the weight of the brake pipe hoses maintains a relative alignment between the connected "glad hand" couplings so as to make the connection resistant to accidental separation due to vibration or shock. As a conventional "glad hand" coupling and brake pipe hose are too heavy and unwieldy for use with monitoring equipment, it is desirable to use a special hose coupling incorporating a standard brake pipe hose coupling gasket, as well as a latching mechanism to prevent the accidental separation of the monitoring equipment hose coupling from the vehicle brake pipe hose coupling. In order to safely disconnect the pressurized coupling from the brake pipe hose connector, it is desirable to bleed off the trapped air pressure before disconnection.